They’re not team specific, @Tuaya, so whatever you have equipped at the time the other person starts the fight is what is going to show up for him/her. It’ll probably be a lot like how classes used to function, before they were tied to individual teams.
So during Guild Wars be sure to always have your Cedric medals equipped, and your defenses should be nearly immune to status effects.
But I’m pretty sure this is how it’s currently intended. Salty said medals would apply to players’ defenses somewhere—I can try to track down the post if you want?
EDIT: Found it in the Patch Notes thread: 4.6 Update Patch Notes - #121 by Saltypatra